Drill Cuttings Transfer System and Related Methods

ABSTRACT

A system for handling drill cuttings conveys cuttings into bulk tanks via a conduit. The bulk tanks have a lower portion that converges to an elongated opening. A conveyance member positioned at the elongated opening forces the cuttings out of a discharge port at the bottom of the bulk tank. Once suitable conveyance member is a screw-type conveyor coupled to a motor that applies a motive force to the cuttings. The bulk tank lower portion can be formed as a wedge or trough that generally conforms to the configuration of the conveyance member. The bulk tanks hold the cuttings until it can be discharged via the discharge port to a transport vessel for processing or disposal. For offshore operations, the system includes a separation unit on the rig that forms the cuttings from fluid returning from the wellbore and a cuttings flow unit that conveys the cuttings from the separation unit to the bulk tanks.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application takes priority from U.S. Provisional Patent ApplicationSer. No. 60/789,395, filed Apr. 5, 2006.

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

This disclosure relates generally to handling of waste materials,especially particulate drill solids.

2. Description of the Related Art

In the drilling of oil and gas wells, drilling fluids or “muds” are usedto provide well bore lubrication, to cool the drill bit, to protectagainst corrosion and to provide a pressure head to maintain formationintegrity. There are two main types of drilling muds: water-based andoil-based. Generally, surface pumps circulate drilling mud down thetubular drill string. The mud exits at the drill bit and flows up theannulus between the drill string and the bore. The returning fluid (orreturn fluid) carries the drill cuttings away from the bit and out ofthe wellbore. Oil-based drilling muds are stable oil external-waterinternal emulsions including wetting agents to hold solids such as drillcuttings in the oil phase. The drill cuttings thus tend to become oilwet, trapping large quantities of oil-based mud in their intergranularspaces and creating environmental concerns regarding disposal of theoil-contaminated drill cuttings.

In the prior art, drill cuttings contaminated with oil-based drillingmuds were often collected in settling tanks where re-usable drilling mudwas drawn off the top of the tank and contaminated drill cuttings, asbottoms, were transported to appropriate disposal sites. Such storageand transportation operations are costly and environmentally undesirableespecially in offshore drilling operations. Typically, oil-contaminatedcuttings contain about fifty percent (50%) by volume of oil-basedliquid. The value of this large volume of entrained oily liquids isconsiderable, and there is a strong incentive to recover the oil-baseddrilling mud both for economic as well as environmental reasons.

Accordingly, the cuttings are commonly separated from the drilling fluidby devices such as shale shakers, which remove cuttings and large solidsfrom the drilling fluid during the circulation thereof. Basically, sucha device has a sloping, close mesh screen over which fluid returningfrom the hole being drilled passes. The solids captured on the screentravel down the sloping surface to be collected in the shaker ditch orcuttings trough. It is also desirable to recover as much of theexpensive drilling fluids as possible. Therefore, other devices, whichplay a role in the separation of solids from drilling fluids, includecyclone separators and centrifuges. The cuttings discharged from theshakers, cyclones and centrifuges that are collected in the shaker ditchor cuttings trough are still highly contaminated with the drillingfluids and therefore form a slurry or heavy sludge. Typically the slurryis conveyed into containers or skips, which are then periodically movedby crane from the rig onto a vessel.

This process is disadvantageous for a number of reasons. First, theskips take up considerable valuable space on the rig floor. Moreover,the handling of the skips requires the use of the rig crane, which maydivert the crane from other important duties. One prior art device usesa pneumatic conveyance arrangement to convey materials out of a bulktank that has a conical hopper section. It is believed that one drawbackof such an arrangement is that using pressurized air as a sole means fordischarging cuttings may not adequately evacuate the bulk tank ofcuttings. It is believed that another drawback is that the circularopening of the conical hopper section could get plugged with cuttings.

The present disclosure addresses these and other drawbacks of the priorart.

SUMMARY OF THE DISCLOSURE

In aspects, the present disclosure provides efficient systems andmethods for processing, storing and transporting drill cuttings that aregenerated while drilling hydrocarbon-producing wellbores. These cuttingsas noted earlier are entrained in a drilling fluid returning from thewellbore (return fluid). After the return fluid is separated to form aslurry of cuttings, the cuttings are conveyed into one or more bulktanks via conduits such as hoses, pipes or tubing. The bulk tank has alower portion that converges to an elongated opening at which a cuttingsconveyance member is positioned. To discharge cuttings, the cuttingsconveyance member, when energized, applies a motive force that causesthe cuttings to flow out of a bulk tank discharge port to a transferline. As the cuttings flow out of the bottom of the tank, gravity pullsmore cuttings into the cuttings conveyance member. The cuttingsconveyance member may be operated in a first mode to flow cuttings and asecond mode to mix cuttings. One suitable cuttings conveyance memberincludes a rotating screw-type conveyor or auger coupled to a motor.

In one embodiment, the lower portion of the bulk tank has a wedge ortrough shape that feeds cuttings to the cuttings conveyance member. Incontrast to a conical shaped lower portion that is defined by a singleinclined wall that converges to a circular exit opening, the wedgeshaped lower portion is defined by at least two walls that converge toan elongated slot-like exit opening. Advantageously, due to itsrelatively large size, the elongated slot-like exit opening is lesssusceptible to plugging during discharge operations. Additionally, theelongated slot-like exit opening can be configured to conform with ahorizontally aligned cuttings conveyance member such that cuttings areevenly fed into the cuttings conveyance member.

To further assist the discharge of cuttings out of the bulk tank,pressurized air can be fed into one or more locations in the bulk tank.One function for this pressurized air is to balance the pressure betweenthe bulk tank and devices connected to the bulk tank. In somearrangements, the cuttings conveyance member feeds cuttings into atransfer line in communication with a pneumatic flow device. Thepneumatic flow device uses high pressure air to propel cuttings alongthe transfer line. To prevent back flow of cuttings into the tank, itmay be desirable to balance the pressure inside the tank with thepressure at the pneumatic flow device. Thus, in one aspect, pressurizedair is fed into the bulk tank at a pressure value that compensates forincreased pressures generated by the pneumatic flow device. In anotheraspect, pressurized air can be used to fluidize the cuttings in the bulktank. For example, when the cuttings have been kept in the bulk tank foran extended time, the weight of the cuttings can force liquids to flowout of the cuttings at the bottom of the tank. Thus, a form ofstratification occurs wherein a relatively dense cuttings layer formsalong the interior surfaces of the lower portion of the bulk tank. Thisdense cuttings layer can slow or even choke off the flow of cuttings outof the bulk tank. To break up or reduce the viscosity of this relativelydense cuttings layer, pressurized gas such as air can be introduced atone or more points near the lower portion of the bulk tank. Theinflowing gas penetrates this relatively dense cuttings layer andreduces its density and/or physically displaces this layer. In onearrangement, a first pressurized gas line at a top of the tank pressurebalances the tank and a second pressurized gas line fluidizes therelatively dense cuttings layer. In another arrangement, the pressurizedgas line for fluidizing the relatively dense cuttings layer provides gasat a pressure value that also pressure balances the bulk tank.

In one arrangement suited for offshore operations, the system includes aseparation unit on the rig that forms the slurry of cuttings. Theseparation unit can include one or more shakers, centrifuge-typeseparators and/or other suitable devices. A cuttings flow unit conveysthe cuttings from the separation unit to the bulk tanks or otherselected location. The cuttings flow unit can include, for example, anauger type conveyor and pump or blower device to flow the cuttings andone or more diverter valves that can direct the cuttings flow as needed.In one arrangement, a controller controls the flow of cuttings into theplurality of bulk tanks. Sensors positioned on each of the bulk tanksproduce signals indicative of the volume of cuttings in an associatedbulk tank. The controller controls the flow of cuttings in response tothe sensor signals. The bulk tanks can be filled simultaneously,sequentially or by any other scheme. The bulk tanks can hold thecuttings until it can be discharged to a transport vessel or vehicle forprocessing and/or disposal. The transport vessel or vehicle can have abank of containers adapted to receive the cuttings from the bulk tanks.

Examples of the more important features of the disclosure have beensummarized (albeit rather broadly) in order that the detaileddescription thereof that follows may be better understood and in orderthat the contributions they represent to the art may be appreciated.There are, of course, additional features of the disclosure that will bedescribed hereinafter and which will form the subject of the claimsappended hereto.

BRIEF DESCRIPTION OF THE FIGURES

For detailed understanding of the present disclosure, reference shouldbe made to the following detailed description of the preferredembodiment, taken in conjunction with the accompanying drawing:

FIG. 1 schematically illustrates a system for processing, storing andoffloading drill cuttings made in accordance with one embodiment of thepresent disclosure;

FIG. 2A schematically illustrates a side view of a bulk tank inaccordance with one embodiment of the present disclosure;

FIG. 2 b schematically illustrates an end view of a bulk tank inaccordance with one embodiment of the present disclosure;

FIG. 3 schematically illustrates an wedge shaped lower section of a bulktank made in accordance with one embodiment of the present disclosure;

FIG. 4 schematically illustrates a bulk tank and pressurized air supplysystem in accordance with one embodiment of the present disclosure; and

FIG. 5 schematically illustrates a bulk tank in accordance with oneembodiment of the present disclosure used in an offshore drillingenvironment.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure relates to devices and methods for processing,storing and transporting a slurry of drill cuttings. The presentdisclosure is susceptible to embodiments of different forms. There areshown in the drawings, and herein will be described in detail, specificembodiments of the present disclosure with the understanding that thepresent disclosure is to be considered an exemplification of theprinciples of the disclosure, and is not intended to limit thedisclosure to that illustrated and described herein. Further, none ofthe described elements or combination of elements should be consideredessential features of the present teachings unless the descriptionexpressly describes the element or combination of elements as essential.

As shown in FIG. 1, in one embodiment particularly suited for use on anoffshore drilling rig, a cuttings handling system 10 may include aseparation unit 12, cuttings flow units 14, 15, and one or more bulktanks 16. The system offloads the cuttings to one or more suitablecontainers 18 on a transport vessel (not shown). In one mode ofoperation, the system receives return fluid, which has entrainedcuttings, from a wellbore being drilled. The separations unit 12separates some of the drilling fluid from the return fluid for re-use infurther drilling and also forms a slurry of cuttings. The cuttings flowunit 14 conveys the cuttings via a conduit 20 to the bank of bulk tanks16. After the bulk tanks 16 are filled with cuttings, a mechanicallydriven and gravity assisted conveyance member discharges the cuttingsfrom the bulk tanks 16. The cuttings flow unit 15 propels the dischargedcuttings via a transfer line 22 to the container(s) 18 or bulk tanks ofthe transport vessel (not shown). Thus, in contrast to conventionalcuttings handling arrangements, less human intervention is needed tocollect, store and move drill cuttings on a rig. The elements making upthe FIG. 1 embodiment are discussed in further detail below.

The separations unit 12 extracts the relatively expensive drilling fluidfrom the return fluid. In one arrangement, the separations unit 12 caninclude one or more shale shakers 21. Within the shale shaker 21, thereturn fluid and entrained solids are discharged over a vibratoryseparator that has one or a series of tiered screens. The screens catchand remove solids from the return fluid flowing therethrough. Theseparations unit 12 can also include other separation devices, such as acentrifugal separator 22, that are also configured to extract drillingfluid from the cuttings. Such separation devices and techniques areknown in the art and will not be discussed in further detail. Theeffluent or output of the separations unit 12 is a relatively viscousslurry made up of oil or additive-covered rock, earth and debris. Theterms cuttings and slurry will be used interchangeably.

The cuttings flow unit 14 transports the cuttings from the separationsunit 12 to other devices such as the bulk tanks 16 or another locationsuch as the vessel storage tanks 18. In one embodiment, the cuttingsflow unit 14 includes an auger-type device that continually conveys thecuttings to a dense phase blower 24 that impels the cuttings through aconduit 20 such as piping or hoses. Suitable valves such as a divertervalve can be used in the conduit 20 to selectively direct flow of thecuttings.

Referring now to FIGS. 1 and 2A-B, the bulk tanks 16 receive and storethe flow of cuttings from the conduit 20. The tanks 16 have an uppercylindrical portion 26 and a lower portion 28 that converges to anelongated opening 29. In a manner described in further detail below, thelower portion 28 promotes mass flow of cuttings through the tank 16.Positioned at a bottom end of the lower portion 28 is a conveyancemember 32 that applies a motive force that impels the cuttings out ofthe bulk tanks 16. Pressurized gas, such as air, from a source 34 is fedinto one or more locations in the bulk tank 16 to maintain a pressurebalance in the system 10 and/or to fluidize the cuttings in the bulktank 16.

The filling of the bulk tanks 16 can be controlled manually,automatically or a combination thereof. In one arrangement, a controller35 receives signals from sensors 36 positioned on the bulk tanks 16. Thesensor signals indicate the amount of cuttings in the bulk tanks 16.Thus, in one arrangement, a controller 35 can have a programmable logiccircuit (PLC) that directs flow into a bulk tank 16 until the associatedsensor 36 indicates that the bulk tank 16 is full. Thereafter, the PLCstops flow to the bulk tank 16 by actuating appropriate valves andinitiates flow into the next bulk tank 16. This process can continueuntil all of the bulk tanks 16 are filled. While a sequential fillingprocess has been described, it should be appreciated that two or morebulk tanks 16 can be filled at the same time. While in some embodiments,the tank can be constructed to hold 100 BBL of drill cuttings having aspecific gravity of 2.34, other sizes and configurations can also beused.

As explained earlier, the slurry of cuttings can be relatively viscousand not flow effectively under the effect of only gravity. Therefore,the conveyance member 32 forcibly impels the cuttings out of the bulktanks 16. In one embodiment, the conveyance member 32 is a rotatingscrew conveyor driven by a motor drive 33. A screw flight portionextends horizontally along a long axis of the wedge shaped portion 28.Rotation of the screw propels the cuttings to the transfer line 22 andthe cuttings flow unit 15. In some arrangements, the conveyance member32 is right and left hand reversible. In the right hand rotation mode,the cuttings flow downward to a port 36. In the left hand rotation mode,the cuttings are mixed to maintain material consistency. This isadvantageous when the cuttings are stored for long periods of time,since heavier material will settle to the tank bottom and lighter fluidswill flow to the top. This stratification of materials can make itdifficult to empty the tank of the cuttings. In such circumstances, theleft hand rotation will mix the cuttings and enable the cuttings to flowout of the tank. In still other embodiments, two or more conveyancemembers can cooperate to expel the cuttings out of the bulk tank 16. Ascrew or auger is merely one illustrative member suitable for applying amotive force throughout the body of the cuttings. It should beappreciated that the conveyance member 32 positioned within the bulktank is susceptible to numerous variations that can adequately apply amotive force to expel the cuttings out of the bulk tank 16. For example,suitable conveyance mechanisms include pneumatic systems, progressivecavity pumps, and vacuum pumping systems.

Referring now to FIGS. 2A-B and 3, the lower portion 28 cooperates withthe conveyance member 32 to discharge flow out of the tank 16. In oneembodiment, the lower portion 28 has a wedge, chisel or trough shapethat is generally defined by two sets of walls 40 and 42. Forconvenience, such a shape will be referred to as a wedge shape. Each setof walls 40 and 42 has an associated angle 46 and 48 from horizontal,respectively. The angles 46 and 48 are selected such that the firstdrill cuttings that enter into the tank are the first drill cuttings toexit the tank, i.e., mass flow. The walls 40 and 42 converge to theopening 29 that is longitudinally aligned with the conveyance member 32.As should be appreciated, in contrast to a conical shaped section thatconverges to a circular opening, the opening 29 presents a relativelylarge elongated slot-like cross-sectional flow area through which thecuttings can flow. Thus, there is a reduced risk that cuttings canocclude or plug the opening 29. Furthermore, it should also beappreciated that the wedge shaped portion 28 and elongated opening 29can evenly distribute cuttings across a relatively large portion of theconveyance member 32. Other elongated or non-conical shapes can also beused in certain applications.

In an exemplary operating mode for discharging cuttings, gravity pullsthe cuttings into the conveyance member 32, which then conveys thecuttings out of the tank 16. As the cuttings exit the tank 16,additional cuttings fall into the conveyance member 32. Advantageously,the wedge shaped portion 28 cause a mass flow of cuttings thatsubstantially uniformly loads the conveyance member 32 during thisprocess. Thus, in one aspect, the system 10 discharges cuttings out ofthe tank 16 using a mechanically driven and gravity assistedarrangement.

To support the cutting discharge operation, there is shown in FIG. 4 asource 60 that provides pressurized gas such as air for pressurebalancing the tank 16 and/or fluidizing the cuttings in the tank 16. Inone embodiment, ports 62 a and 62 b that are coupled to the source 60via suitable conduits 64 introduce pressurized gas at one or more pointsalong the bulk tank 16. One or more of the ports 62 a can be positionedto break up or reduce the viscosity of settled cuttings that layer theinterior surfaces of the lower wedge shaped portion 28. The gas flowingthrough such ports 62 a penetrates this relatively dense cuttings layerand reduces its overall density. That is, the gas intermixes with or“fluffs” the cuttings layer. The inflowing gas can also physicallydisplace or dislodge portions of this layer from the interior surfacesof the tank 16. One or more ports 62 b can also be positioned at or neara top of the tank 16 to provide pressure balancing gas. In the FIG. 4embodiment, the source 60 operates as the cuttings flow unit 15 (FIG. 1)by supplying high pressure gas to propel cuttings through the transferline 22. For example, the source 60 can supply a continuous flow of highpressure air into the transfer line 22 at the same time the conveyancemember 32 (FIG. 2A) feeds cuttings into the transfer line 22. Becausethe source 60 and the bulk tanks 16 are in fluid communication via thetransfer line 22, the high pressure gas in the transfer line 22 canapply a back pressure at the tank 16. This applied back pressure canrestrict the flow of cuttings out of the tank 16. To compensate for theoperating pressure generated by the source 60, pressurized gas fedthrough the ports 62 b increases the pressure in the tank 16 to at leastpartially offset this applied back pressure. Of course, in certainembodiments, the pressurized gas flowing through ports 62 a can bothfluidize the relatively dense cuttings layer and provide gas at apressure value that also pressure balances the bulk tank.

A number of instruments and device can be utilized to control the flowof pressurized gas. For example, valves 70 for selectively feeding gasinto the ports 62 a and 62 b can be controlled by solenoid controls 72.A solenoid 64 control unit can also be used to control a valve 74feeding pressurized air into the transfer line 22. Additionally,suitable gauges 76 such as pressure gauges and level gages can bepositioned as desired on the tank 16. In many applications, thepressurized gas can be air, but other gases such as nitrogen can beused.

Referring now to FIG. 5, there is shown an embodiment of the presentdisclosure that is suited for offshore drilling applications. As isknown, platform, floater, jack up or work over drilling operationsutilize a surface facility such as an offshore rig 70 from which adrilling riser 72 or other device conveys a drill string 74 into asubsurface well (not shown). Positioned on the offshore rig 70 iscuttings handling system 71 that processes the return fluid from thesubsurface wellbore (not shown) using equipment previously discussed andconveys the cuttings to a bank of bulk tanks 76. During drilling, thereturn fluid is processed and the cuttings continuously conveyed andstored in the bulk tanks 76. A controller fills the bulk tanks 76 usingpreprogrammed instructions and signals from suitably positioned sensors.Periodically, a transport vessel 78 such as a barge is moored adjacentto the rig 70 and storage tanks 80 in the barge 78 are connected to thecuttings handling system 71. Thereafter, high pressure gas is fed intothe bulk tanks 76 to fluidize the cuttings and balance the pressure inthe bulk tanks 76. Once the conveyance device 32 (FIG. 2A) is energized,cuttings flow out of the bulk tanks 76 and to the barge 78.

It should be appreciated that the cuttings handling systems describedabove offer enhanced safety due to the reduced number of handlingoperations such as interventions by personnel to hook up containers tothe crane, manual shoveling of cuttings into containers, transfers ofcontainers around the rig floor, use of the crane rig, etc. Furthermore,the transport vessel to which the cuttings is offloaded is onlytemporarily moored adjacent the rig. A continuously moored transportvessel could pose a hazard to the rig and itself during rough seas.Thus, reducing the time the transport vessel is moored to the rig alsoreduces the risk that inclement weather will interfere with drillingoperations.

While the foregoing disclosure is directed to the preferred embodimentsof the disclosure, various modifications will be apparent to thoseskilled in the art. It is intended that all variations within the scopeof the appended claims be embraced by the foregoing disclosure.

1. A system for handling a return fluid formed of drilling fluid andentrained cuttings recovered while drilling a wellbore in an earthenformation, comprising: (a) a separation unit at least partiallyseparating the drilling fluid from the return fluid, a slurry ofcuttings thereby being formed; (b) a cuttings flow unit receiving thecuttings from the separation unit, the cutting flow unit conveying thecuttings through a conduit coupled thereto; (c) at least one tankcoupled to the conduit, the tank having a lower portion converging to anelongated opening; and (d) a conveyance member positioned adjacent tothe elongated opening receiving the cuttings from the lower portion andflowing the cuttings out of the at least one bulk tank.
 2. The system ofclaim 1, further comprising a flow device receiving the flow of cuttingsfrom the conveyance member and conveying the cuttings to a selectedlocation.
 3. The system of claim 2, further comprising a gas sourceproviding a pressurized gas to the at least one tank to at leastpartially offset a pressure increase associated with operation of thecuttings flow device.
 4. The system of claim 1, further comprising a gassource providing a gas to the at least one tank to fluidize at least aportion of the cuttings in the at least one tank.
 5. The system of claim1, wherein the lower portion is wedge shaped and wherein the conveyancemember includes an auger longitudinally aligned with the elongatedopening.
 6. The system of claim 1, wherein the at least one tankincludes a cylindrical upper portion, the cuttings flowing from theupper portion to the lower portion.
 7. The system of claim 1 wherein theconveyance member operates in a first mode to flow the cuttings and asecond mode to mix the cuttings.
 8. A method for handling a return fluidformed of drilling fluid and entrained cuttings recovered while drillinga wellbore in an earthen formation, comprising: (a) separating thedrilling fluid from the return fluid to form a slurry of cuttings with aseparation unit; (b) conveying the cuttings through a conduit coupled tothe separation unit using a cuttings flow unit; (c) receiving thecuttings into at least one tank coupled to the conduit, the bulk tankhaving a lower portion converging to an elongated opening; and (d)flowing the cuttings out of the at least one tank using a conveyancemember positioned adjacent to the elongated opening.
 9. The method ofclaim 8, further comprising conveying the cuttings to a selectedlocation using a flow device that receives the flow of cuttings from theconveyance member.
 10. The method of claim 9, further at least partiallyoffsetting a pressure increase associated with operation of the flowdevice using a gas source that provides a pressurized gas to the atleast one tank.
 11. The method of claim 8, further comprising fluidizingat least a portion of the cuttings in the at least one tank using a gassource that provides a gas to the at least one tank.
 12. The method ofclaim 8, wherein the lower portion is wedge shaped and wherein theconveyance member includes an auger longitudinally aligned with theelongated opening.
 13. The method of claim 8, wherein the at least onetank includes a cylindrical upper portion, the cuttings flowing from thecylindrical upper portion to the lower portion.
 14. The method of claim8 further comprising operating the conveyance member in a first mode toflow the cuttings and a second mode to mix the cuttings.
 15. A systemfor handling cuttings separated from a return fluid formed of drillingfluid and entrained cuttings, comprising: (a) a tank for receiving thecuttings, the tank having a cylindrical upper portion and a wedge shapedlower portion converging to an elongated opening; and (b) a conveyancemember positioned adjacent to the elongated opening receiving thecuttings from the wedge shaped lower portion and flowing the cuttingsout of the tank.
 16. The system of claim 15, further comprising a flowdevice receiving the flow of cuttings from the conveyance member andconveying the cuttings to a selected location.
 17. The system of claim16, further comprising a gas source providing a pressurized gas to thetank to at least partially offset a pressure increase associated withoperation of the cuttings flow device.
 18. The system of claim 15,further comprising a gas source providing a gas to the tank to fluidizeat least a portion of the cuttings in the tank.
 19. The system of claim15 wherein the conveyance member operates in a first mode to flow thecuttings and a second mode to mix the cuttings.
 20. The system of claim15 wherein the lower portion is defined by a first set of walls and asecond set of walls, each of the walls of the first and second set ofwalls having an angle selected to cause mass flow of the cuttings.